Saint Isidore was a Roman naval officer who served during the time of the emperor Decius. The persecutions being officially conducted during this period compelled him to keep his Christianity secret on pain of death, though. His ship was docked at the Greek island of Chios at the beginning of the season of lent, and Isidore wished to celebrate the start of the season with his fellow Christians at a church on the island. Because he was slightly less careful than normal in seeking out a church, though, his movements were detected by another Roman sailor who in turn reported it to one of Isidore's superiors, a man named Numerius. Numerius confronted Isidore about his Christianity, and Isidore responded that he was glad that the secret was out so that he no longer had to lead a dual life, keeping his Christianity secret. Numerius then had Isidore stripped of his rank, beaten without mercy, and killed. The Romans, with typical ancient Roman disregard for sanitation, dumped his body into a cistern, from which Saint Myrope later retrieved it.
In art, Saint Isidore is usually depicted as a bearded layman in early Christian garb being dragged over rocks by a horse, although he is also depicted variously as being in a ship with two companions, meeting three ladies at the gates of Chios, arguing with the devil, baptizing a woman, or being beheaded. He died around 250 C.E., and his feastday is May 14. A chapel was built by Saint Marcian in the fifth century over Isidore's grave, at which he is still venerated to this day. Isidore's relics, however, were removed to the church of St. Mark in Venice in 1525 and have remained there since.
Sources: http://saintgeorge.org/news_and_events/church_calendar/saint_of_the_day/05may/may14.php3, http://users.erols.com/saintpat/ss/0515.htm